I don't know if the fuck dolls are alive or not, because the whole game has a really dark story, when you look at what you do to a whole galaxy.
From the gameplay they are the whores of your poorest customers, the same as you have 3 different stages of bar modules in your station, it is the same for your brothel, poor, medium and rich.
There are also the brothel arcade stations for your disobedient slaves, which are inbetween the fuckdolls and the private rooms but seem to me to be a bit of a special case, because you use them to break your slaves and make money at the same time.
Although i'm not really sure if the game makes a distinction for your customers between poor and rich or if it just generates customers with a random value of money to spend.